jQuery addClass example

Change class name on click in jQuery

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<script src="https://rawgit.com/tinymce/tinymce-dist/master/tinymce.min.js"></script>
<script src="https://rawgit.com/tinymce/tinymce-dist/master/jquery.tinymce.min.js"></script>

<button>Click Me</button>
<textarea id="mytextarea">Hello, World!<div>hello word in div</div></textarea>

JavaScript

tinymce.init({
    selector: '#mytextarea'
});

$('button').on('click', function(e) {
    $('#mytextarea').tinymce().$('body div').css("border","1px solid red");
});